Messages in this thread Patch in this message | | | Date | Tue, 16 Oct 2018 16:37:50 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: perf's handling of unfindable user symbols... |
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Em Tue, Oct 16, 2018 at 12:02:30PM -0700, David Miller escreveu: > From: Arnaldo Carvalho de Melo <acme@redhat.com> > Date: Tue, 16 Oct 2018 15:45:06 -0300 > > > Exec summary: yeah, drop that hack, I agree, patch at the end of the > > message.
> > So, I thought something had changed and in the past we would somehow > > find that address in the kallsyms, but I couldn't find anything to back > > that up, the patch introducing this is over a decade old, lots of things > > changed, so I was just thinking I was missing something.
> > I tried a gtod busy loop to generate vdso activity and added a 'perf > > probe' at that branch, on x86_64 to see if it ever gets hit:
> Good, thanks for doing the detailed checking!
> > In the process I noticed a bug, we're only have records for '[vdso]' for > > pre-existing commands, i.e. ones that are running when we start 'perf top', > > when we will generate the PERF_RECORD_MMAP by looking at /perf/PID/maps. > > Hmmm. vdso mappings are installed by __install_special_mapping()
Yeah, the kernel is ok, tooling seems b0rken, will check.
[root@jouet ~]# perf record ~acme/c/gtod ^C[ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.076 MB perf.data (1499 samples) ]
[root@jouet ~]# perf report -D | grep PERF_RECORD_MMAP2 71293612401913 0x11b48 [0x70]: PERF_RECORD_MMAP2 25484/25484: [0x400000(0x1000) @ 0 fd:02 1137 541179306]: r-xp /home/acme/c/gtod 71293612419012 0x11be0 [0x70]: PERF_RECORD_MMAP2 25484/25484: [0x7fa4a2783000(0x227000) @ 0 fd:00 3146370 854107250]: r-xp /usr/lib64/ld-2.26.so 71293612432110 0x11c50 [0x60]: PERF_RECORD_MMAP2 25484/25484: [0x7ffcdb53a000(0x2000) @ 0 00:00 0 0]: r-xp [vdso] 71293612509944 0x11cb0 [0x70]: PERF_RECORD_MMAP2 25484/25484: [0x7fa4a23cd000(0x3b6000) @ 0 fd:00 3149723 262067164]: r-xp /usr/lib64/libc-2.26.so [root@jouet ~]#
And using tools/perf/python/twatch.py enabling mmap = 1:
<SNIP> cpu: 1, pid: 25743, tid: 25743 { type: comm, pid: 25743, tid: 25743, comm: gtod } cpu: 2, pid: 25742, tid: 25742 { type: mmap, pid: 25742, tid: 25742, start: 0x55d0a916e000, length: 0x219000, offset: 0, filename: /usr/bin/procmail } cpu: 1, pid: 25743, tid: 25743 { type: mmap, pid: 25743, tid: 25743, start: 0x400000, length: 0x1000, offset: 0, filename: /home/acme/c/gtod } cpu: 2, pid: 25742, tid: 25742 { type: mmap, pid: 25742, tid: 25742, start: 0x7fa6d666e000, length: 0x227000, offset: 0, filename: /usr/lib64/ld-2.26.so } cpu: 1, pid: 25743, tid: 25743 { type: mmap, pid: 25743, tid: 25743, start: 0x7f7774286000, length: 0x227000, offset: 0, filename: /usr/lib64/ld-2.26.so } cpu: 2, pid: 25742, tid: 25742 { type: mmap, pid: 25742, tid: 25742, start: 0x7ffd673d6000, length: 0x2000, offset: 0, filename: [vdso] } cpu: 1, pid: 25743, tid: 25743 { type: mmap, pid: 25743, tid: 25743, start: 0x7fff8f7ad000, length: 0x2000, offset: 0, filename: [vdso] } <SNIP>
> which should be emitting proper mmap events by calling > perf_event_mmap(vma). > Maybe the event is emitted too early? It doesn't look like it. These > are emitted after load_elf_binary() iterates over the PHDRs and > mmap()'s those areas of the binary, and we definitely see those events > properly. > > > The kernel doesn't seem to be generating a PERF_RECORD_MMAP for vDSOs... And > > we can't do this in 'perf record' because we don't process event by event, just > > dump things from the ring buffer to a file... > It should be, see above.
Yeah, I'll check why is that the tooling side doesn't seem to be catching those...
> > diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c > > index 0988eb3b844b..bc646185f8d9 100644 > > --- a/tools/perf/util/event.c > > +++ b/tools/perf/util/event.c > > @@ -1561,26 +1561,9 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr, > > > > return NULL; > > } > > -try_again: > > + > > al->map = map_groups__find(mg, al->addr); > > - if (al->map == NULL) { > > - /* > > - * If this is outside of all known maps, and is a negative > > - * address, try to look it up in the kernel dso, as it might be > > - * a vsyscall or vdso (which executes in user-mode). > > - * > > - * XXX This is nasty, we should have a symbol list in the > > - * "[vdso]" dso, but for now lets use the old trick of looking > > - * in the whole kernel symbol list. > > - */ > > - if (cpumode == PERF_RECORD_MISC_USER && machine && > > - mg != &machine->kmaps && > > - machine__kernel_ip(machine, al->addr)) { > > - mg = &machine->kmaps; > > - load_map = true; > > - goto try_again; > > - } > > - } else { > > + if (al->map != NULL) { > > /* > > * Kernel maps might be changed when loading symbols so loading > > * must be done prior to using kernel maps. > > > > > > Acked-by: David S. Miller <davem@davemloft.net>
Reported-by: Suggested-by:
:-)
OK, will get this with a nice cover letter and stash into my perf/urgent branch.
- Arnaldo
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